(a) Field of the Invention
The present invention relates to an optical code reading device. More specifically, the present invention provides an optical code reading device using one or more optical fibers for transmitting light from a light source to a scanning head of the device.
(b) Description of the Prior Art
Code reading devices of handy scanner type for reading characters and various kinds of code such as bar codes have been known.
The handy scanner comprises a housing of a predetermined shape suitable for operating by hand, a light source for illuminating an object to be read, an optical system for receiving reflection light reflected from the object and for forming an image of the object, a sensor for converting the optical image obtained by the optical signal into an electrical signal and a circuit arrangement for processing the electric signal from the sensor to produce a digital signal in a binary form or binary decimal form. A one dimensional image sensor or two dimensional image sensor may be used. The use of two dimensional image sensor enables the object of two dimensions to be read in an instant. When a one dimensional image sensor is used, the object is read by scanning sequentially in a direction of the array of the photo sensor cells of the image sensor. The scanning in the direction of the array of the photo sensor cells is referred to as a main scanning. In order to read the object, the scanner is moved in a direction perpendicular to the main scanning direction, so that the two dimensional object can be read. In case the inage sensor having one dimension or two dimension is used as the sensor of the code reading device, the resolution of reading the object depends on the size of the unit photo sensor cells. Moreover, since it is required to illuminate a region expanding in one dimension or two dimensions when the sensor of one dimension or two dimension image sensor is used, an incadescent lamp is used as the light source and the light is dispersed. Thus the light source can be deemed as a surface light source.
A photo diode may be used as a sensor for reading object code. In this case the scanner may be moved in one dimension or two dimensions to obtain the image information of the object. By measuring the amount of the movement of the scanner, the point corresponding to the photo diode output can be identified.
When a photo diode is used as the sensor, it is impossible to obtain the image information of the object at two points simultaneously but it is possible to obtain the image information of the object at only one point simultaneously. In this arrangement, it is necessary to concentratedly illuminate the light beam on one point of the object with the remainder of the object unilluminated so as to detect the reflection light only from the point illuminated by the photo diode. The diameter of the light beam defines the resolution of reading the code. Therefore, it is important to illuminate the object reducing the spot size of the light beam as small as possible.
In the conventional code reading device using the photo diode as the sensor, the light projected from a light source is directly concentrated by a lens system so that the spot size is throttled and the throttled light is projected directly to the object.
The light projected on the object is reflected and the reflected light is received by the photo diode which generates the information of the intensity of the reflected light. Since a portion of the object which is not illuminated does not generate reflection light, no effect is revealed on the output of the photo diode with respect to any pattern on that portion.
As mentioned above, the resolution of reading of the object is decided by the spot size of the illumination light, therefore, it is desired to make the spot size as small as possible.
The spot size of the light projected from the light is more or less wide and in many cases the shape of the spot of the light is not a true circle but is deformed from the true circle. Therefore, even if the projected light is concentrated by the lens system, it is difficult to throttle the light into a desirably fine beam. Accordingly, the resolution of reading the object in the reading device can not be improved.
Moreover, the scanning head of the conventional code reading device is provided with a light source and a rotatable mirror to direct the light beam of the light source toward a light projection window of the scanning head so that the light beam can be projected from the window to scan the object.
The conventional arrangement mentioned above must provide the rotational mirror in the scan head as a part of the optical system. Moreover, if the rotational mirror collects moisture or foreign matters, the reflection light from the mirror is reduced. In addition, according to the distribution of the stain of the mirror, the light intensity of the mirror is changed, whereby it becomes impossible to identify the object code and a reading error may occur.
Moreover, since the mirror and light source are provided in the scanning head, it is difficult to reduce the weight and size of the scanning head.
Moreover, in the conventional code reading device, when a semiconductor laser is used for the reading light, since the reading light is infra red light with the wave length less than 750 nm which is invisible to the human eyes. In case a gas laser such as Ar laser or He-Ne laser is used as the light source, since the spot size of the light is very small, it is difficult to see the light beam.
In this case, in order to see the reading light (defined as reading .SIGMA.), there is proposed to attach an auxiliary light or sighting light . In this arrangement, in the prior art, two light sources of the light .SIGMA. and are disposed in a rectangular relation and both lights are combined using a half mirror. However, employment of the half mirror in the path of the reading light .SIGMA. causes the intensity of the reading light to be decreased and spot size of the reading light at the object to be read is expanded and the resolution is decreased. Moreover, employment of the half mirror in the scanning head makes the scanning head bulky. Moreover, an adjustment between the axes of the reading light and sighting light is required.